1. Field of the Invention
The present invention relates to a robot cleaner for automatic operation, and more particularly, to a coordinate compensation method for an automatic robot cleaner.
2. Description of the Related Art
A robot cleaner generally determines the target area of cleaning operation using sensors such as ultrasound sensor mounted on a main body, or in accordance with information input by a user. The robot cleaner then plans a most efficient path of cleaning operation. According to the plan, the robot cleaner runs and drives a dust sucking part to draw in dust from the floor.
One way of moving such a robot cleaner along the planned path is that the robot cleaner calculates the current location using absolute coordinate system. Another method is that the robot cleaner runs based on a relative coordinate system using running distance and rotation angle with respect to a reference location of the cleaning area.
According to one example of using the absolute coordinate system, a robot cleaner captures through a CCD camera the images of objects on the ceiling such as ceiling lamp, or location recognition marks which may be separately installed on the ceiling, and accordingly detects its current location based on the captured images. Using the CCD camera, however, causes problems of high costs because it requires the system to fast process a large amount of data.
According to one example of using the relative coordinate system, a robot cleaner is equipped with a running distance sensor and an angle sensor which can detect rotational angle of the robot cleaner. An encoder is generally used as the running distance sensor to detect number of rotation of the wheels, and a gyro sensor, which is capable of detecting relative angle, is generally used as the angle sensor. It is simple to control when using the gyro sensor because the robot cleaner can rotate at a precise angle as desired. However, such a gyro sensor usually has a detection error ranging from 5% to 10%, and a problem occurs as the robot cleaner repeats rotation operation because the detection error accumulates. As a result, the robot cleaner may not follow the planned path accurately.
FIG. 1 shows, in a rather exaggerated manner, the running path of the robot cleaner deviating from the planned path due to detection error of the gyro sensor. A robot cleaner 1 begins from the starting point S and runs straightforward as calculated to the spot A. Using the gyro sensor, the robot cleaner 1 rotates by 90°, runs straightforward as calculated and therefore, arrives at the spot B. At this time, the robot cleaner 1 misses the intended destination, that is, the spot B, but instead arrives at spot B′. The robot cleaner 1 rotates by 90° using the gyro sensor, and moves straightforward as calculated, and perceives to have arrived at the spot C. However, again due to detection error of the gyro sensor, the robot cleaner 1 actually does not follow the planned path, but instead reaches the deviated spot C′. As the detection error accumulates, the deviation is greater at the spots C, C′ than the spots B, B′. The robot cleaner 1 moves through the spots D, E, F and G in sequence, with incrementing detection error of the gyro sensor. As a result, the robot cleaner 1 is deviated from the planned path more and more as it operates further. When the robot cleaner 1 finishes cleaning operation, there remain certain areas which have not been cleaned.